Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$51.98	5.316%	$54.7433	$54.74	$54.75	$54.70
Purchase #2	$142.60	3.689%	$147.8605	$147.86	$147.85	$147.90
Purchase #3	$134.42	9.871%	$147.6886	$147.69	$147.70	$147.70
Purchase #4	$46.45	11.639%	$51.8563	$51.86	$51.85	$51.90
Purchase #5	$93.74	4.435%	$97.8974	$97.90	$97.90	$97.90
Purchase #6	$136.39	8.152%	$147.5085	$147.51	$147.50	$147.50
Purchase #7	$83.89	6.374%	$89.2371	$89.24	$89.25	$89.20
7 purchase totals =	$689.47		$736.7917	$736.80	$736.80	$736.80